01 - 
                Preheat the oven to 350°F. Grease a 9x13 inch pan with nonstick cooking spray. Set aside.
              
              
              
                02 - 
                In a large bowl, mix together the melted butter, brown sugar and granulated sugar with a hand mixer until blended. Add in the eggs and vanilla extract until incorporated. Add in the peanut butter, and continue to beat until combined.
              
              
              
                03 - 
                In a separate bowl, whisk together the salt and flour. Slowly add to your wet mixture and mix until just combined.
              
              
              
                04 - 
                Spread the batter into the prepared pan. Bake for 25 to 30 minutes until golden and a toothpick inserted in the center comes out clean. Remove the bars from the oven and let cool completely.
              
              
              
                05 - 
                To make the frosting, in a large bowl beat together the softened butter and marshmallow fluff. Add in the powdered sugar 1 cup at a time until blended.
              
              
              
                06 - 
                Spread the frosting on the cooled bars, and sprinkle chopped peanuts on top.